Redox mechanism in the NiP2 electrode for Li-ion batteries:: A DFT study coupled with local chemical bond analyses

Li reactivity of the monoclinic NiP(2) electrode is investigated through first-principles density functional theory calculations and local chemical bond analysis. The stability of various Li (x) NiP(2) is studied with respect to the conversion reaction NiP(2) + 6Li -> 2Li(3) + Ni degrees. The T = 0K Li (x)NiP(2) phase stability diagram, as obtained, reveals that several ternary phases of lithium composition Li(2)NiP(2) can be electrochemically achieved upon reduction. They correspond to monoclinic or tetragonal structures in which Ni adopts a square-planar (D(4h)-Li(2)NiP(2)) or a pseudo-tetrahedral (Td-Li(2)NiP(2)) environment. A local chemical bond analysis suggests that D(4h)-Li(2)NiP(2) would result from an interlayer P-P bond breaking induced by a two-phase (P redox) process, while Td-Li(2)NiP(2) would result from a Jahn-Teller distortion associated with a single-phase (Ni-P redox) process.